This paper reviews the development of focal reducer imaging systems for use with interferometers and telescopes. Some less widely known designs are also discussed, these are based on the work of the author in the 1970s, while at the Royal Observatory, Edinburgh and at the University of Manchester. Interest in this type of optical system has come about particularly with the development of image intensifiers and electronic detector array such as CCDs. These designs are of interest wherever image reduction is required. Great Britain.